Multidimensional Structural Access

ABSTRACT

Multiple planes within the sample are exposed from a single perspective for contact by an electrical probe. The sample can be milled at a non-orthogonal angle to expose different layers as sloped surfaces. The sloped edges of multiple, parallel conductor planes provide access to the multiple levels from above. The planes can be accessed, for example, for contacting with an electrical probe for applying or sensing a voltage. The level of an exposed layer to be contacted can be identified, for example, by counting down the exposed layers from the sample surface, since the non-orthogonal mill makes all layers visible from above. Alternatively, the sample can be milled orthogonally to the surface, and then tilted and/or rotated to provide access to multiple levels of the device. The milling is preferably performed away from the region of interest, to provide electrical access to the region while minimizing damage to the region.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to processing of multidimensional,microscopic structures to provide electrical access to internalstructures.

BACKGROUND OF THE INVENTION

As semiconductor fabrication processes pack more circuitry into smallerpackages, integrated circuit (IC) designs are becoming morethree-dimensional (3D). It is difficult to measure, analyze and locatefaults in 3D microscopic (including nanoscopic) structures.

An engineer will typically identify a region-of-interest (ROI) that hewants to investigate, based upon, for example, aberrant electricalbehavior of a circuit component. Most ROIs in conventional ICs areconfined to a small volume of the device in a planar region. Forexample, a static random access memory (SRAM) or a conventional“not-and” (NAND) flash cell each occupies a distinct X and Y location,with a small volume of active area in the Z direction. An engineertypically identifies the ROI by starting with a logic bit or gateaddress, which can then be mapped to a physical X/Y location in anactive region of the structure.

The ROI is often buried below layers of insulator and conductors. Oncethe ROI is identified, the circuit can be “deprocessed,” that is,overlying structures can be removed, to expose the ROI. Currentdeprocessing techniques typically provide access to the structure in aplanar fashion ion beam milling creates surfaces orthogonal to thedevice surface in order to allow imaging, probing, or other localizationtechniques. Likewise cleaving the wafer or parallel-lapping deprocessingprovides access to a plane of the structure.

Techniques to analyze the ROI include, for example, micro-probing, inwhich conductive probes are contacted to the conductors on the IC toapply and/or measure voltages or currents. Another technique foranalyzing a ROI is voltage contrast imaging, in which a charged particlebeam image, which is sensitive to any voltage on the imaged surface, isobtained while a voltage is applied to a part of the circuit. Otheranalysis techniques include scanning probe microscopy, such asscanning-capacitance microscopy, in which a fine probe is scanned abovethe region of interest and the electrical or physical behavior of theprobe is monitored. As used herein, analysis techniques include imagingtechniques.

Current techniques map locations on an integrated circuit as if thedevice were a city in which buildings have only one floor simply gettingthe street address is sufficient to deliver the mail to the correctlocation. Emerging three dimensional (3D) IC fabrication technologies donot constrain the active area (i.e., transistor or memory cell) to oneplane in the Z direction—active areas occupy many levels of 3D devices.The city map is now populated by skyscrapers the address informationneeds to reference to which floor the mail is to be delivered. Ratherthan identify a 2D region of interest, an engineer will require distinctisolation of a volume-of-interest (VOI) in three dimensions.

For 3D IC structures, prior art techniques that provide planar accessare inherently limited to two dimensions of the structure, resulting ineither more complicated or impossible final access to the VOI.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides electrical access tointernal components of a three-dimensional structure.

Multiple planes within the sample are exposed from a single perspectivefor imaging and/or probing. For example, the sample can be milled at anon-orthogonal angle to expose different layers as sloped surfaces. Thenon-orthogonal milling exposes edges of multiple, parallel conductorplanes to provide access to multiple levels from above. Once exposed,the planes can be accessed, for example, for contacting with anelectrical probe for applying or sensing a voltage. The level of anexposed layer to be contacted can be identified, for example, bycounting down the exposed layers from the sample surface, since thenon-orthogonal mill makes all layers visible from above. Alternatively,the sample can be milled orthogonally to the surface, and then tiltedand/or rotated to provide access to multiple levels of the device. Themilling is preferably performed away from the region of interest, toprovide electrical access to the region while minimizing damage to theregion.

Additional processing can be applied to the exposed layers, for example,using circuit edit-type techniques, such as passivating, depositing aninsulator on part of the sample, cutting circuits, and depositingconductors to change behavior or creating probing points.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter. It should be appreciated by those skilled in the art thatthe conception and specific embodiments disclosed may be readilyutilized as a basis for modifying or designing other structures forcarrying out the same purposes of the present invention. It should alsobe realized by those skilled in the art that such equivalentconstructions do not depart from the spirit and scope of the inventionas set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more thorough understanding of the present invention, andadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is shows a 3D storage device having a trench milled therein toexpose a vertical face;

FIG. 2 is a top-down view of the 3D storage device of FIG. 1;

FIG. 3 shows a 3D storage device milled in accordance with an embodimentof the present invention;

FIG. 4 is a top-down view showing the storage device of FIG. 3;

FIG. 5 shows a portion of a tilted workpiece that provides access toburied conductive layers without requiring milling at an angle to thework piece surface;

FIG. 6 is a flowchart showing the steps of an embodiment of theinvention; and

FIG. 7 shows schematically a dual beam system that can be used toimplement the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In one conventional analysis of two-dimensional processing, a region ofinterest is exposed by ion beam milling and electrical probes arecontacted to the region of interest, typically from above. The region ofinterest can be viewed from above using an electron beam with voltageapplied for voltage contrast imaging. This works well for 2D structures,but for newer structures having transistors or memory cells on manylayers, it is very difficult to access the correct layer in the stackwhen one is looking at the structure from the top. In accordance with anaspect of some embodiments of the invention, the sample is milled and/ortilted so that multiple planes within the sample are exposed from asingle perspective, typically from above, for imaging or probing.

Also, most prior art cross-sectional techniques are preformed throughthe region of interest, such as the particular failing part in a failureanalysis. Due to the increased complexity of new 3D structures it isadvantageous to keep as much of the structure around the region ofinterest intact during analysis. In accordance with an aspect of someembodiments of the invention, the milling exposes the electricalconnections to a ROI, and keeps much of the ROI intact while providingelectrical access to the ROI. As used herein, the term ROI or region ofinterest is also used to refer to a volume of interest or VOI.

Off-angle mills, preferably from about 30° to about 45° from a normal tothe surface, spatially separate out the layers in a top-down view sothat they may be viewed and accessed. The greater the deviation fromorthogonality, the more surface is exposed to a vertical view from abovethe sample. A normal to the exposed area has a component in the verticaldirection, so that the horizontal layer can be observed from above andcontacted from above by an electrical probe. A tilted sample can providethe same effect, separating out layers for viewing and exposing them ina top down view.

By milling in an orientation that is not orthogonal to the work piecesurface or tilting the structure after a vertical mill, users can seethe electrical addressing connections to the ROI using an opticalmicroscope or a SEM and can provide therefore electrical signals to theROI without being able to actually see it. The tapered mills or tiltedsample provide access to the sample in angled sidewalls to allowelectrical localization of a defect or other ROI. Access to the angledside wall allows probing the plane at the z-depth of interest, whilestill providing access to the vertical conductor. Embodiments of theinvention provide access to X, Y, and Z localization from a top-view ofa sample, and allow electrical probing access to the VOI using currenttop-down probing techniques.

After the milling, angled or vertical, the sample is oriented so thatboth the milled face and top surface of the sample can be viewed and/orelectrically probed. The viewing and probing are used, for example, forvoltage contrast imaging, electrical characterization by probingdifferent layers and observing the electrical response using diagnosticequipment, sensing atomic force microscope probe, or observation ofphotonic emission.

FIG. 1 shows a 3D storage device 100 having a trench milled therein toexpose a vertical cross section. Such devices are typically encapsulatedin glass (not shown). Vertical conductors 102 make electricalconnections to vertically aligned elements in different horizontallayers. Patterned horizontal conductors 104 make connections in the x-yplane. Each of the three labeled conductors 104 contacts circuitelements in the same Y-Z plane (i.e., having the same x coordinate), butin different Z-planes. FIG. 1 shows a section milled out to expose aface 106. To make connections to face 106 requires a contact coming infrom the side, rather than top down. It is difficult to see andmanipulate a probe to provide the side access because the side ofexposed vertical face is not visible from a top-down view and mostprobes are designed to contact a conductor from above. FIG. 2 is atop-down view of the 3D storage device. Note that while an X-Y locationcan be observed, no Z information is available from a top-down view ofthe milled face 106. In such a case, there is no reliable method ofidentifying if the defect is in the top layer or somewhere lower in thedevice stack.

FIG. 3 shows a storage device 300 having angled mills in accordance withan embodiment of the invention that produces sloped sides 302 and 304,allowing for much easier electrical contact than the vertical face 106of FIG. 1. FIG. 4 is a top-down view showing the angled milled surfaces302 and 304 of device. The X-Y locations of contact points is easy todetermine, as are the Z positions of the contact points in the stack. Bymaking the various layers at different Z positions available forobservation in the sloped faces, the conductor plane corresponding tothe exact Z layer of interest may be identified and contacted to providean electrical contact to the VOI. FIG. 4 shows electrical probes 402Aand 402B that contact the exposed edge of internal conductors that arein electrical contact with the region of interest. Probe 402C contacts avertical conductor 102 that is in electrical contact with the region ofinterest. The probes move horizontally under manual control or undercontrol of an automated controller to a desired location, and then canmove in the Z-direction, also either manually or under control of acontroller, to be lowered to contact the selected conductive layer at adesired location. Electrical signals can be applied to one or moreprobes, while, for example, other electrical signals are sensed by oneor more other probes, or a voltage contrast image is observed. Theelectrical probes are contacted onto the exposed conductor by loweringfrom above, while the process is being observed from above.

The angled mills expose contacts that allow a particular electricalcomponent to be addressed even though that component itself is notexposed. Thus the component and neighboring components can remainintact. In some embodiments, each electrical structure represents asingle bit, for example, in a 3D NAND or DRAM. The bit can be addressedusing the exposed X and Y connections for the corresponding level, aswell as the corresponding Z connection. The X and Y conductors for anylevel of Z can be easily observed from above when the conductors areexposed by the angled milling or tilted after a normal angle milling.The exposed conductors do not need to be adjacent to the structure ofinterest. A user can observe the number of steps in the angled mill todetermine which Z level the x and y connectors are on by counting downlayers.

Angled milling or tilting exposes the connection so that it can becontacted from above rather than from the side. Milling can be performedusing the ion beam with or without an etch-enhancing glass, asdescribed, for example, in U.S. patent application Ser. No. 13/921,466.

FIG. 5 shows a part of a 3D structure, analogous to the volume of FIG. 3near the intersection of walls 302 and 304. In FIG. 5, however, themilled wall 502 and 504 are vertical. The work piece is then tilted sothat a normal to each of the milled faces 502 and 504 has a component inthe vertical direction. That is, the milled face 502 and 504 are visiblefrom above and so the electrical probes 402A, 402B and 402C can be movedindividually in the horizontal plane to be positioned above selectedconductors and then lowered from above to contact the appropriate layerto provide an electrical connection to the region of interest.Multilayer device 504 is preferably tilted between about 30° to about45°.

FIG. 6 is a flow chart showing the steps of a preferred embodiment ofthe invention. In step 602, a region of interest is identified. Forexample, the ROI may correspond to an element of a device that is foundto perform poorly. The position of the ROI is determined fromcomputer-aid-design information that maps a logic element to anelectrical component and then to a physical location on the device. Instep 604, the device is milled, preferably at an angle between about 30°to about 45°, to expose conductors near the region of interest. In step606, the preferred position of probe contact is determined. For example,the layout of the chip is checked to determine which conductor on whichconductive layer makes contact with the region of interest. Theidentified conductive layer can be identified by counting down from thetop of the chip to the appropriate level, since the angled mill providesvisibility of the multiple levels. In step 608, electrical probes aremoved in the X-Y direction to position the probes appropriately asdetermined in step 606, and then in step 610, the probes are lowered inthe Z direction to contact electrical conductors at or near the regionof interest. It is understood that the probe motion may not be simplerectangular X-Y-Z motion, but the probe will move through space anddownward to contact the electrical conductor. As used here, moving inthe X-Y direction or Z direction does not require separate motions inthe mentioned planes or direction, but includes rotations andsimultaneous motions in different directions that accomplish the sameresult. In step 612, voltages or currents are applied to the samplethrough one or more of the probes. In step 614, the effect of theapplied voltage or current is observed. Observing the effect caninclude, for example, sensing voltages or currents from one or more ofthe probes, observing the region of interest using voltage contrastimaging, micro-Raman analysis, or other imaging or analytical technique.

Additional processing can be applied to the exposed layers, for example,using circuit edit-type techniques, such as passivating, depositing aninsulator on part of the sample, cutting circuits, and depositingconductors to change behavior or creating probing points. Circuitedit-type techniques are well known. For example, a conductor can bedeposited by beam-induced deposition to connect two or more exposedlayers. An insulator can be deposited by beam-induced deposition beforethe conductor deposition to electrically other exposed layers of theintegrated circuit from the deposited conductor. Exposed conductors canalso be cut to with the ion beam to break an electrical contact.

FIG. 7 shows a typical dual beam system 710 suitable for practicing thepresent invention, with a vertically mounted SEM column and a FIB columnmounted at an angle of approximately 52° from the vertical. Suitabledual beam systems are commercially available, for example, from FEICompany, Hillsboro, Oreg., the assignee of the present application.While an example of suitable hardware is provided below, the inventionis not limited to being implemented in any particular type of hardware.

A scanning electron microscope 741, along with power supply and controlunit 745, is provided with the dual beam system 710. An electron beam743 is emitted from a cathode 752 by applying voltage between cathode752 and an anode 754. Electron beam 743 is focused to a fine spot bymeans of a condensing lens 756 and an objective lens 758. Electron beam743 is scanned two-dimensionally on the specimen by means of adeflection coil 760. Operation of condensing lens 756, objective lens758, and deflection coil 760 is controlled by power supply and controlunit 745.

Electron beam 743 can be focused onto substrate 722, which is on movablestage 725 within lower chamber 726. When the electrons in the electronbeam strike substrate 722, secondary electrons are emitted. Thesesecondary electrons are detected by a secondary electron detector 740 asdiscussed below.

Dual beam system 710 also includes focused ion beam (FIB) system 711which comprises an evacuated chamber having an upper portion 712 withinwhich are located an ion source 714 and a focusing column 716 includingextractor electrodes and an electrostatic optical system. The axis offocusing column 716 is tilted 52 degrees from the axis of the electroncolumn. The upper portion 712 includes an ion source 714, an extractionelectrode 715, a focusing element 717, deflection elements 720, and afocused ion beam 718. Ion beam 718 passes from ion source 714 throughfocusing column 716 and between electrostatic deflectors 720 towardsubstrate 722, which comprises, for example, a semiconductor devicepositioned on movable stage 725 within lower chamber 726.

Stage 725 can preferably move in a horizontal plane (X and Y axes) andvertically (Z axis). Stage 725 can also tilt approximately 60° androtate about the Z axis. A door 761 is opened for inserting substrate722 onto X-Y stage 725 and also for servicing an internal gas supplyreservoir, if one is used. The door is interlocked so that it cannot beopened if the system is under vacuum.

An ion pump (not shown) is employed for evacuating upper portion 712.The chamber 726 is evacuated with turbomolecular and mechanical pumpingsystem 730 under the control of vacuum controller 732. The vacuum systemprovides within chamber 726 a vacuum of between approximately 1×10⁻⁷Torr and 5×10⁻⁴ Torr. If an etch-assisting gas, an etch-retarding gas,or a deposition precursor gas is used, the chamber background pressuremay rise, typically to about 1×10⁻⁵ Torr.

The high voltage power supply provides an appropriate accelerationvoltage to electrodes in ion beam focusing column focusing 716 forenergizing and focusing ion beam 718. When it strikes substrate 722,material is sputtered, that is physically ejected, from the sample.Alternatively, ion beam 718 can decompose a precursor gas to deposit amaterial.

High voltage power supply 734 is connected to liquid metal ion source714 as well as to appropriate electrodes in ion beam focusing column 716for forming an approximately 1 keV to 60 keV ion beam 718 and directingthe same toward a sample. Deflection controller and amplifier 736,operated in accordance with a prescribed pattern provided by patterngenerator 738, is coupled to deflection plates 720 whereby ion beam 718may be controlled manually or automatically to trace out a correspondingpattern on the upper surface of substrate 722. In some systems thedeflection plates are placed before the final lens, as is well known inthe art. Beam blanking electrodes (not shown) within ion beam focusingcolumn 716 cause ion beam 718 to impact onto blanking aperture (notshown) instead of substrate 722 when a blanking controller (not shown)applies a blanking voltage to the blanking electrode.

The liquid metal ion source 714 typically provides a metal ion beam ofgallium. The source typically is capable of being focused into a subone-tenth micrometer wide beam at substrate 722 for either modifying thesubstrate 722 by ion milling, enhanced etch, material deposition, or forthe purpose of imaging the substrate 722. Other ion sources, such as aplasma ion source, can also be used.

A probe assembly includes a probe motion mechanism 780 and probe tips781. The probe tips can be moved individually to a desired position andlowered to contact the substrate 722. While three probe tips are shown,the number of probe tips can vary. Multiple probe motion mechanism canbe used to control any number of probes. The probe tips can apply avoltage or current to the substrate 722 at a precise location and/or cansense a voltage or current. In some embodiments, the probes are mountedon a ring around the work piece.

A charged particle detector 740, such as an Everhart-Thornley detectoror multi-channel plate, used for detecting secondary ion or electronemission is connected to a video circuit 742 that supplies drive signalsto video monitor 744 and receives deflection signals from controller719. The location of charged particle detector 740 within lower chamber726 can vary in different embodiments. For example, a charged particledetector 740 can be coaxial with the ion beam and include a hole forallowing the ion beam to pass. In other embodiments, secondary particlescan be collected through a final lens and then diverted off axis forcollection.

An optical microscope 751 allows observation of the sample 722 and theprobes 781. The optical microscope may be co-axial with one of thecharged particle beams, as described, for example, in U.S. Pat. No.6,373,070 to Rasmussen, for “Method apparatus for a coaxial opticalmicroscope with focused ion beam,” is assigned to the applicant of thepresent application.

A gas delivery system 746 extends into lower chamber 726 for introducingand directing a gaseous vapor toward substrate 722. U.S. Pat. No.5,851,413, to Casella et al. for “Gas Delivery Systems for Particle BeamProcessing,” assigned to the assignee of the present invention,describes a suitable gas delivery system 746. Another gas deliverysystem is described in U.S. Pat. No. 5,435,850, to Rasmussen for a “GasInjection System,” also assigned to the assignee of the presentinvention. For example, a metal organic compound can be delivered to thebeam impact point to deposit a metal upon impact of the ion beam or theelectron beam. A precursor gas, such as (CH₃)₃Pt(C_(p)CH₃) to depositplatinum or tungsten hexcarbonyl to deposit tungsten, can be deliveredto be decomposed by the electron beam to provide the protective layer instep 108.

A system controller 719 controls the operations of the various parts ofdual beam system 710. Through system controller 719, a user can causeion beam 718 or electron beam 743 to be scanned in a desired mannerthrough commands entered into a conventional user interface (not shown).Alternatively, system controller 719 may control dual beam system 710 inaccordance with programmed instructions. A preferred controller is incommunication with or includes a memory that stores instructions forautomatically carrying out the steps of FIG. 6. System controller 719can be used to control the probe motion assembly 780. In someembodiments, dual beam system 710 incorporates image recognitionsoftware, such as software commercially available from CognexCorporation, Natick, Mass., to automatically identify regions ofinterest, and then the system can manually or automatically expose crosssections for imaging in accordance with the invention. For example, thesystem could automatically locate similar features on semiconductorwafers including multiple devices, and expose and form images offeatures of interest on different (or the same) devices.

The invention has broad applicability and can provide many benefits asdescribed and shown in the examples above. The embodiments will varygreatly depending upon the specific application, and not everyembodiment will provide all of the benefits and meet all of theobjectives that are achievable by the invention. Particle beam systemssuitable for carrying out the present invention are commerciallyavailable, for example, from FEI Company, the assignee of the presentapplication.

Descriptions herein use the terms horizontal and vertical relative to awafer or other work piece. It will be understood that “horizontal”typically is used to mean parallel to the work piece surface and theconductive planes deposited on to the work piece, and “vertical” istypically used to mean orthogonal to the work piece surface.

The invention has broad applicability and can provide many benefits asdescribed and shown in the examples above. The embodiments will varygreatly depending upon the specific application, and not everyembodiment will provide all of the benefits and meet all of theobjectives that are achievable by the invention. Particle beam systemssuitable for carrying out the present invention are commerciallyavailable, for example, from FEI Company, the assignee of the presentapplication.

The present specification discloses both a method and an apparatus forperforming the operations of the method. Such apparatus may be speciallyconstructed for the required purposes, or may comprise a general purposecomputer or other device selectively activated or reconfigured by acomputer program stored in the computer. Various general purpose chargedparticle beam systems may be used with programs in accordance with theteachings herein. Alternatively, the construction of more specializedapparatus to perform the required method steps may be appropriate.

In addition, the present specification also implicitly discloses acomputer program, in that it would be apparent to the person skilled inthe art that the individual steps of the method described herein may beput into effect by computer code. The computer program is not intendedto be limited to any particular programming language and implementationthereof. It will be appreciated that a variety of programming languagesand coding thereof may be used to implement the teachings of thedisclosure contained herein. Moreover, the computer program is notintended to be limited to any particular control flow. There are manyother variants of the computer program, which can use different controlflows without departing from the spirit or scope of the invention.

Such a computer program may be stored on any computer readable medium.The computer readable medium may include storage devices such asmagnetic or optical disks, memory chips, or other storage devicessuitable for interfacing with a general purpose computer. The computerreadable medium may also include a hard-wired medium such as exemplifiedin the Internet system, or wireless medium such as exemplified in theGSM mobile telephone system. The computer program when loaded andexecuted on such a general-purpose computer or controller for a chargedparticle beam and effectively results in an apparatus that implementsthe steps of the preferred method.

The invention may also be implemented as hardware modules. Moreparticular, in the hardware sense, a module is a functional hardwareunit designed for use with other components or modules. For example, amodule may be implemented using discrete electronic components, or itcan form a portion of an entire electronic circuit such as anApplication Specific Integrated Circuit (ASIC). Numerous otherpossibilities exist. Those skilled in the art will appreciate that thesystem can also be implemented as a combination of hardware and softwaremodules.

Although much of the previous description is directed at semiconductorwafers, the invention could be applied to any suitable substrate orsurface. Further, whenever the terms “automatic,” “automated,” orsimilar terms are used herein, those terms will be understood to includemanual initiation of the automatic or automated process or step. In thefollowing discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . . ”

To the extent that any term is not specially defined in thisspecification, the intent is that the term is to be given its plain andordinary meaning. The accompanying drawings are intended to aid inunderstanding the present invention and, unless otherwise indicated, arenot drawn to scale.

The term “integrated circuit” refers to a set of electronic componentsand their interconnections (internal electrical circuit elements,collectively) that are patterned on the surface of a microchip. The term“semiconductor chip” refers generically to an integrated circuit (IC),which may be integral to a semiconductor wafer, separated from a wafer,or packaged for use on a circuit board. The term “FIB” or “focused ionbeam” is used herein to refer to any collimated ion beam, including abeam focused by ion optics and shaped ion beams.

The embodiment above describes 3D NAND type structures, but theinvention is not limited to such structures and is useful, for example,for DRAMS, and for characterizing trenches and other structures, as wellas circular holes.

To the extent that any term is not specially defined in thisspecification, the intent is that the term is to be given its plain andordinary meaning. The accompanying drawings are intended to aid inunderstanding the present invention and, unless otherwise indicated, arenot drawn to scale.

Some embodiments of the invention provide a method of analyzing a regionof interest in a three dimensional integrated circuit structure havingmultiple layers of conductive materials, comprising directing a focusedion beam toward the three dimensional integrated circuit structure at anon-normal angle to the layers of conductive material to expose multiplehorizontal conductive layers; determining which exposed horizontalconductor corresponds to the vertical position of a component ofinterest; moving one or more electrical probes to contact the exposedhorizontal conductor from above; applying a voltage to the electricalprobe; and observing the effect of the applied voltage to analyze theregion of interest.

In some embodiments, directing a focused ion beam toward the threedimensional integrated circuit structure includes directing the focusedion beam to leave the region of interest intact while expose multiplehorizontal conductive layers to provide electrical access to the regionof interest.

In some embodiments, moving one or more electrical probes to contact theexposed horizontal conductor includes moving one or more of theelectrical probes to position the probed over the exposed horizontalconductor and then moving the probe in a direction having a verticalcomponent to contact the exposed horizontal conductor.

In some embodiments, the three dimensional structure comprises a datastorage circuit.

In some embodiments, the three dimensional structure comprises a Logiccircuit and/or a NAND, a SRAM, a DRAM, or a memory cell.

Some embodiment provide a method of analyzing a region of interest in athree dimensional integrated circuit structure, comprising directing afocused ion beam toward the three dimensional integrated circuitstructure to mill a surface exposing multiple horizontal conductivelayers; determining which exposed horizontal conductive layercorresponds to the vertical position of a region of interest; loweringan electrical probe to contact a conductor that is in the determinedhorizontal conductive layer and that corresponds to a region ofinterest; applying a voltage to the electrical probe; and observing theeffect of the applied voltage to analyze the region of interest.

In some embodiments, directing a focused ion beam toward the threedimensional integrated circuit structure to mill a surface exposingmultiple horizontal conductive layers includes directing the focused ionbeam normal to the work piece surface and the embodiment furthercomprises tilting the work piece so that a normal to the milled surfacehas a vertical component.

In some embodiments, tilting the work piece includes tilting the workpiece at an angle of between about 30° to about 45°.

In some embodiments, directing a focused ion beam toward the threedimensional integrated circuit structure to mill a surface exposingmultiple horizontal conductive layers includes directing the focused ionbeam at a non-normal angle to the horizontal conductive layers.

In some embodiments, directing the focused ion beam at a non-normalangle to the horizontal conductive layers includes directing the focusedion beam at an angle of between about 30° to about 45° to the horizontalconductive layers.

In some embodiments, observing the effect of the applied voltage toanalyze the region of interest includes using voltage contrast imaging,sensing an electrical signal, or using an atomic force microscope probe.

In some embodiments, sensing an electrical signal comprises sensing avoltage or current using an electrical probe or probes.

Some embodiments provide a system for analyzing a region of interest ina three-dimensional integrated circuit, comprising an ion optical columnfor providing a focused beam of ions; an electron optical column forproviding a focused beam of electrons; a particle detector for detectingsecondary particles emitted from the sample; an electrical probe movablein three dimensions for contacting the integrated circuit and providingelectrical contact to the region of interest; a controller communicatingto a computer memory, the computer memory storing instructions fordirecting a focused ion beam toward the three dimensional integratedcircuit structure to mill a surface exposing multiple horizontalconductive layers; determining which exposed horizontal conductive layercorresponds to the vertical position of a region of interest; loweringan electrical probe to contact a conductor that is in the determinedhorizontal conductive layer and that corresponds to a region ofinterest; applying a voltage to the electrical probe; and observing theeffect of the applied voltage to analyze the region of interest.

In some embodiments, the computer instructors for directing the focusedion beam toward the three dimensional integrated circuit structureincludes computer instruction for directing the focused ion beam at anon-normal angle to the horizontal conductive layers.

In some embodiments, the computer instructors for directing the focusedion beam toward the three dimensional integrated circuit structureincludes directing the focused ion beam normal to the work piece surfaceand further comprise computer instructions for tilting the work piece sothat a normal to the milled surface has a vertical component.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

We claim as follows:
 1. A method of analyzing a region of interest in athree dimensional integrated circuit structure having multiple layers ofconductive materials, comprising: directing a focused ion beam towardthe three dimensional integrated circuit structure at a non-normal angleto the layers of conductive material to expose multiple horizontalconductive layers; determining which exposed horizontal conductorcorresponds to the vertical position of a component of interest; movingone or more electrical probes to contact the exposed horizontalconductor from above; applying a voltage to the electrical probe; andobserving the effect of the applied voltage to analyze the region ofinterest.
 2. The method of claim 1 in which directing a focused ion beamtoward the three dimensional integrated circuit structure includesdirecting the focused ion beam to leave the region of interest intactwhile exposing multiple horizontal conductive layers to provideelectrical access to the region of interest.
 3. The method of claim 1 inwhich moving one or more electrical probes to contact the exposedhorizontal conductor includes moving one or more of the electricalprobes to position the probe over the exposed horizontal conductor andthen moving the probe in a direction having a vertical component tocontact the exposed horizontal conductor.
 4. The method of claim 1 inwhich directing a focused ion beam at a non-normal angle to the layersof conductive material surface includes directing the focused ion beamat an angle of between about 30° to about 45° from a normal to thesurface.
 5. The method of claim 1 in which observing the effect of theapplied voltage includes analyzing the region of interest using voltagecontrast imaging, sensing an electrical signal, or using an atomic forcemicroscope probe.
 6. The method of claim 5 in which sensing anelectrical signal comprises sensing a voltage or current using anelectrical probe or probes.
 7. The method of any of claim 1 in which thethree dimensional structure comprises a data storage circuit.
 8. Themethod of claim 1 in which the three dimensional structure comprises aLogic circuit and/or a NAND, a SRAM, a DRAM, or a memory cell.
 9. Amethod of analyzing a region of interest in a three dimensionalintegrated circuit structure, comprising: directing a focused ion beamtoward the three dimensional integrated circuit structure to mill asurface exposing multiple horizontal conductive layers; determiningwhich exposed horizontal conductive layer corresponds to the verticalposition of a region of interest; lowering an electrical probe tocontact a conductor that is in the determined horizontal conductivelayer and that corresponds to a region of interest; applying a voltageto the electrical probe; and observing the effect of the applied voltageto analyze the region of interest.
 10. The method of claim 9 in whichdirecting a focused ion beam toward the three dimensional integratedcircuit structure to mill a surface exposing multiple horizontalconductive layers includes directing the focused ion beam normal to thework piece surface and further comprising tilting the work piece so thata normal to the milled surface has a vertical component.
 11. The methodof claim 10 in which tilting the work piece includes tilting the workpiece at an angle of between about 30° to about 45°.
 12. The method ofclaim 9 in which directing a focused ion beam toward the threedimensional integrated circuit structure to mill a surface exposingmultiple horizontal conductive layers includes directing the focused ionbeam at a non-normal angle to the horizontal conductive layers.
 13. Themethod of claim 12 in which directing the focused ion beam at anon-normal angle to the horizontal conductive layers includes directingthe focused ion beam at an angle of between about 30° to about 45° tothe horizontal conductive layers.
 14. The method of claim 9 in whichobserving the effect of the applied voltage to analyze the region ofinterest includes using voltage contrast imaging, sensing an electricalsignal, or using an atomic force microscope probe.
 15. The method ofclaim 14 in which sensing an electrical signal comprises sensing avoltage or current using an electrical probe or probes.
 16. A system foranalyzing a region of interest in a three-dimensional integratedcircuit, comprising: an ion optical column for providing a focused beamof ions; an electron optical column for providing a focused beam ofelectrons; a particle detector for detecting secondary particles emittedfrom the sample; an electrical probe movable in three dimensions forcontacting the integrated circuit and providing electrical contact tothe region of interest; a controller communicating to a computer memory,the computer memory storing instructions for: directing a focused ionbeam toward the three dimensional integrated circuit structure to mill asurface exposing multiple horizontal conductive layers; determiningwhich exposed horizontal conductive layer corresponds to the verticalposition of a region of interest; lowering an electrical probe tocontact a conductor that is in the determined horizontal conductivelayer and that corresponds to a region of interest; applying a voltageto the electrical probe; and observing the effect of the applied voltageto analyze the region of interest.
 17. The system of claim 16 in whichthe computer instructors for directing the focused ion beam toward thethree dimensional integrated circuit structure includes computerinstruction for directing the focused ion beam at a non-normal angle tothe horizontal conductive layers.
 18. The system of claim 16 in whichthe computer instructors for directing the focused ion beam toward thethree dimensional integrated circuit structure includes directing thefocused ion beam normal to the work piece surface and further comprisingcomputer instructions for tilting the work piece so that a normal to themilled surface has a vertical component.